Even bigger change came with the rise of social networks and various web apps. Every day more content is hidden in the walled gardens of the web, like Facebook or Twitter, behind the fence of login and password. Just think about it: how much interesting content have you discovered in your friend’s updates, notes and tweets? This content is invisible to Google and other search engines, it’s not backed up by wayback machine or proxy servers. The number of people seeing only the things recommended by their social circle is growing.

Well gosh, a decade ago, Google wasn't indexing my conversations with friends after a golf game, either. How private conversations on Facebook and Twitter differ from that sort of thing is an exercise left to the sane....